What is the Lachman Test?
The Lachman test is performed for the diagnosis of the injuries that can occur at the level of the anterior cruciate ligament, providing a high accuracy rate for acute ruptures of this specific ligament. It is a clinical orthopedic test, being appreciated for its reliability and sensitivity. In comparison to the anterior drawer test or the pivot shift test, the Lachman test is considered to be superior, providing a more accurate assessment of the state in which the anterior cruciate ligament is found.
The test is often used as a rapid on-side assessment method of acute knee injuries but also in the clinical setting, in patients who complain of different degrees of knee pain. The test is named after the person who invented it, meaning John Lachman, an orthopedic surgeon. The Lachman test is one of the passive accessory movement tests that can be used in order to determine any instability in the knee, especially in the sagittal plane.
For the Lachman test, the patient is required to lie down in a supine position, keeping the affected knee slightly flexed (20°-30° of flexion) and the leg externally rotated (in order to relax the IT band). The amount of flexion that is required for the Lachman test is less painful than the flexion required in the anterior drawer test (90°); the advantage of this test is that, by being less painful, the risk of spasms in the hamstrings muscles is reduced. There is one more thing you should know about the chosen position for the Lachman test – the 20°-30° of flexion place the anterior cruciate ligament in a position of maximum stress; thus, the assessment is highly accurate, as there are no other structures to limit the anterior translation movement of the tibia.
The therapist performing the test will have one hand on the thigh of the patient, grasping it, while the other hand is located on the calf. The most essential thing is that the thumb of the therapist is placed precisely on the tuberosity of the tibia.
After positioning his/her hands as it was mentioned above, the therapist will pull the tibia in a forward direction and try to identify how much the tibia moves in the anterior direction. In making this assessment, the therapist will permanently compare the movements of the tibia with the ones of the femur. The displacement in mm in the affected knee can also be compared to the healthy side. In case of severe pain, the Lachman test can be performed under local anesthesia, allowing for a better assessment of the movements in the area.
One of the things that one should pay close attention to is the joint angle at which the test is performed. If the position chosen for the Lachman test is closer to the complete extension of the knee, it means that the anterior translation of the tibia will be naturally reduced. This will automatically lead to a false end point, providing an incorrect diagnosis.
The Lachman test can either deliver a positive or a negative result. If the anterior cruciate ligament is intact, the therapist will encounter a resistance when trying to pull the tibia in a forward direction. This resistance is often described as the firm endpoint, preventing the forward and transitional movements in the tibia. If there is no damage to the anterior cruciate ligament, the Lachman test is negative.
On the other hand, if the anterior cruciate ligament is damaged, the tibia will be characterized by movement and translation in the anterior direction. There is no resistance to the force applied by the therapist, which automatically translates to no endpoint or to an endpoint that is soft. In this situation, when the anterior cruciate ligament is no longer intact and the knee is affected, the Lachman test is positive.
The Lachman test can also provide a negative result in case of a chronic rupture of the anterior cruciate ligament, as the body compensated for the existing problems by attaching the stump of the anterior cruciate ligament to the posterior cruciate ligament. Also, the Lachman test might appear positive even if the patient’s anterior cruciate ligament is intact – this happens when the posterior cruciate ligament is ruptured or damaged. One can identify the rupture of the posterior cruciate ligament by checking the movements of the tibia in the posterior direction, before assessing the anterior ones.
Lachman Test Pictures
If the therapist identifies over 2 mm of anterior translation, this means that the anterior cruciate ligament is torn. There is no resistance to the anterior translation movement and the endpoint is soft. The more the tibia can be translated into the anterior direction, the higher the damage of the anterior cruciate ligament. Serious damage exists when the tibia can be translated into the anterior direction with 10 mm. Therapists make avail of the modern measurement instruments, such as the KT-1000, allowing them to determine exactly how many millimeters can the tibia be translated into the anterior direction.
The manual exam allows for the grading to be classified as such:
- Mild – between 0 and 5 mm displacement (always in comparison to the healthy knee)
- Moderate – between 6 and 10 mm displacement
- Severe – between 11 and 15 mm displacement
- Attention – if the Lachman test demonstrates such a large displacement, besides the rupture of the anterior cruciate ligament, one should also consider the existence of MCL tear or a tear in the knee meniscus
With the KT-1000, the diagnosis of anterior cruciate ligament tear can be made, especially if there is over 11 mm displacement in the affected knee. The same diagnosis can be made if there is a difference of over 3 mm in comparison to the healthy knee. This measurement tool can also be used after the reconstruction of the anterior cruciate ligament – in order to provide a negative result of the test, there should be less than 3 mm displacement, compared to the healthy knee.
Even though the Lachman test delivers high accuracy, it should not the only test used for the diagnosis of the anterior cruciate ligament rupture.